1. Field of the Invention
The present invention relates to a method of fabricating a nozzle plate comprising a base plate provided with a nozzle hole and a water-repellent film formed on one surface of the nozzle plate.
2. Description of Related Art
Known ink jet printers have a print head with a nozzle plate provided with a nozzle hole. However, in operation, ink droplets are unable to travel in the correct direction or be ejected at all if part of the surface of the nozzle plate around the nozzle hole is wet with the ink. To overcome these problems, an invention disclosed in European Patent No. 359365 provides a nozzle plate comprising a plate provided with a nozzle hole and a water-repellent film formed on one surface of the plate to prevent wetting the surface of the plate with the ink.
When the water-repellent film is formed on the major surface of the plate after forming a nozzle hole in the plate, part of the circumference of the nozzle hole is coated unevenly with the water-repellent film or, in the worst case, the nozzle hole is clogged with the water-repellent film. Consequently, the meniscus of the ink differs from one nozzle plate to another, which varies ink jetting time from one nozzle plate to another. In the worst case, the ink cannot be jetted.
Such a problem may be alleviated by a method that forms the water-repellent film over the major surface of the nozzle plate after perfectly plugging up the nozzle hole with a filling material. However, it is difficult to plug up the nozzle hole perfectly with a filling material. Hence, this method is not practical.
With the foregoing problems in view, U.S. Pat. No. 5,208,604 proposes a method of fabricating a nozzle plate for an ink jet printer comprising steps of forming a water-repellent film over the surface of a plate and forming a discharge hole through the plate and the water-repellent film with an excimer laser beam or the like, in which the plate and the water-repellent film are a dry film (SE-320 manufactured by Tokyo Ohka Kogyo Co., Ltd.) and a polyimide film, respectively. Processing of a polymeric workpiece with an excimer laser beam is a laser ablation processing. According to Chemical Review, vol. 89, no. 6 (1989), American Chemical Society, the mechanism of ablation has three processes as shown in FIGS. 5(A), 5(B) and 5(C). In the process shown in FIG. 5(A), a polymeric workpiece 9 absorbs an excimer laser beam 6 transmitted through a mask 5. High molecules of the polymeric workpiece 9 are disintegrated in the process shown in FIG. 5(B), and the molecules are decomposed and atoms are scattered in the process shown in FIG. 5(C).
Generally, the water-repellent film is formed of a resin having a high water repellency, such as a fluororesin or a silicone resin. However, water-repellent films of fluororesins and silicone resins are very difficult to process with an excimer laser beam because fluororesins and silicone resins do not absorb excimer laser light having a wavelength in the ultraviolet range, such as ArF laser light of 198 nm, KrF laser light of 248 nm or XeKr laser light of 308 nm in wavelength. When a nozzle plate consisting of a plate and a water-repellent film of a fluororesin or a silicone resin formed over the surface of the base plate is exposed to an excimer laser beam, the water-repellent film is not processed by the energy of the excimer laser beam, but by the energy of the decomposed molecules and the scattered atoms of the base plate. Consequently, the water-repellent film cannot satisfactorily be processed. Specifically, burrs of the water-repellent film are formed, and the burrs cause the ejecting direction of ink droplets to vary, which deteriorates print quality.
When the nozzle hole is formed by pressing or drilling, burrs are formed even if the water-repellent film is formed of a resin other than fluororesins and silicone resins, entailing the aforesaid problems.